They'll fight over a divided district that includes south San Joaquin County communities of Tracy and Manteca - new territory for Denham - but also Stanislaus County where Hernandez is not as well-known.

What makes the race so interesting? First, the money. Independent groups are pouring cash into both campaigns - close to $3.5 million combined during September and the first few days of October, according to Federal Election Commission campaign finance reports.

Then, the rhetoric. The candidates have clashed on the usual range of national partisan issues - but have also attacked each other on past tax, business and voting practices.

Finally, new statistics about the district's voter registration show that if everyone voted according to party affiliation, it would be a very tight race indeed. Democrats have less than a 1 percent advantage in the district, down from almost 2 percent in May.

"I think this will be one of a handful of races in the House that is going to be treated as one of the most important and most competitive by both parties," said Nathan Monroe, an associate professor of political science at the University of California, Merced. "My expectation is it will get a lot of attention."

Denham emphasizes his fight against government waste. In his first term he led GOP efforts to investigate the spending habits of the General Services Administration, whose 2010 Las Vegas conference has come under national scrutiny.

While his staff did not respond to requests for an interview, Denham at a candidates forum last week touted his experience, not only two years in Congress but eight years in the state Senate.

"There are big issues on the line, and it's going to take some real strong leadership, somebody who's willing to work with both sides of the aisle whether it's popular or not," said the Gulf War veteran and father of two. "There's no place for partisanship here in the Valley."

Denham said the national debt is America's biggest problem, and supports vice presidential nominee Paul Ryan's budget plan to reduce spending. He said the Valley's unemployment rate is "unacceptable," and supports unshackling small businesses from government regulations.

Hernandez, 50, grew up as a migrant worker before embarking on an ambitious career path that eventually saw him fly on the space shuttle in 2009. He is a father of five and now lives in Manteca.

Hernandez said he wants to invest in education, especially science and technology. This would create a more enticing environment for businesses that right now are exporting jobs overseas, he said.

"It's a different animal, running a campaign and going into space," Hernandez said in an interview. "Both have their challenges, and I think they're equally as hard. ... But what I like about my campaign is it's a grass-roots campaign. It's something folks can identify with, someone who is a Valley native, who has been born and raised in this neighborhood and understands the issues.

"Congress does have its challenges," he added. "When all is said and done, it's not rocket science, and if it is, I've got you covered."

As might be expected while a closely contested election approaches, each campaign has dug up some dirt on the other side. At last week's forum, Denham blasted Hernandez for reportedly not voting in 13 elections (Hernandez has said he often traveled with NASA). Hernandez, in turn, accused Denham, a government waste watchdog, of spending more than $1,000 on hotel rooms (Denham responded that he was traveling around trying to cut waste in government.)

Both accused each other of failing to consistently pay taxes in the past.

It's unclear if the negative campaigning will make a difference, Monroe said. There are many other factors to consider, including some beyond the candidates' control. If Republican voters are enthusiastic about presidential candidate Mitt Romney, for example, increased turnout could tip the scales toward Denham. The opposite is also true.

Denham has the advantage of being the more "local" candidate, living in the center of the district while Hernandez has closer San Joaquin County ties in the far north, Monroe said.

On the other hand, Hernandez can offset that by emphasizing his Valley roots as a migrant worker.

As far as cash, both sides' major expenditures may in effect cancel each other out, Monroe said.

He noted this is only one of several competitive Congressional races in the area. "It's going to be an exciting election for the Valley," Monroe said.